The invention relates to semiconductor manufacturing, and more particularly, to methods and systems for semiconductor work-in-process (WIP) dispatch management.
A typical semiconductor fabrication flow for each product is a highly re-entrant process. Each product flow requires the same equipment resource many times before completion of its production cycle. A conventional semiconductor factory typically includes fabrication tools processing semiconductor wafers for a particular purpose, such as photolithography, chemical-mechanical polishing, or chemical vapor deposition. During manufacture, the semiconductor wafer passes through a series of process steps performed by various fabrication tools. For example, in the production of an integrated semiconductor product, the semiconductor wafer passes through up to 600 process steps. Automated dispatch systems initiate personnel or automated transport systems to transport WIPs, such as wafer lots and banks, to desired destinations such as semiconductor fabrication equipment, metrology instruments or stockers.
In a conventional automated manufacturing process, a dispatch system is responsible for initiating the transport system or facility to transport WIPs to the desired destination directly. Two dispatch rules (a tool dispatch rule and a lot dispatch rule) are commonly used to dispatch wafer lots. Using known algorithms, the tool dispatch rule determines the target stocker or the fabrication tool for given WIPs, and the lot dispatch rule determines the target WIPs for given equipment or stockers. These two dispatch rules both attend to many criteria such as priority, yield rate, load balancing, and stability.
The conventional lot dispatch rules determine the target WIPs to be processed based on criterion without considering load-balance factors, such as WIP priorities, resulting in numerous bottlenecks at tool groups and severe production capability reduction.